i have a nikon d40 with a nikkor af-s 55-200mm zoom,this sigma lens seems
to be great value.Would i notice a big advantage in getting closer to
the object?,i also believe this sigma lens wont autofocus with a d40,would there
be any other recommended budget lens?.
thanks in advance
I believe the D40 cannot autofocus using lenses that don't have a built in motor - which tend to be more expensive.
The sigma 70-300mm f4-5.6 apo dg lens is a nice relatively lightweight lens. I've got a photo of a bittern in flight taken at Minsmere with it somewhere in my gallery (here unfortunately this photo illustrates the major drawback of the lens. Whilst capable of decent photo's it's just not long enough) It's probably the best of the budget zooms however in common with many other zooms its performance at 300mm is significantly worse than between 70 and 280mm. The bittern was at 280mm.
If you're interested in a zoom on a D40 it'll be worth keeping an eye on the Sigma 80-400mm OS. At the moment its around £700. Within the next few months Sigma will be releasing a newer version of this lens and dealers will be desperate to sell off this older model. By late summer it'll be down to circa £500. Whilst the built in lens motor doesn't meet the speed of Sigma's HSM it's adequate enough for most uses. More info
Your other option is the 300mm af-s again circa £700 plus a 1.4x tc (£50 - Kenko, £200 - Nikon). Ultimately this offers the best quality but you lose the ability to zoom. Unfortunately I can't afford this just yet but for an example of what you can get with the older non-afs version this was taken with a D50 Nikon's earlier 6 Mpix entry model.